Thermal transfer systems have been developed to obtain prints from pictures that have been generated electronically, for example, from a color video camera or digital camera. An electronic picture can be subjected to color separation by color filters. The respective color-separated images can be converted into electrical signals. These signals can be operated on to produce cyan, magenta, and yellow electrical signals. These signals can be transmitted to a thermal printer. To obtain a print, a black, cyan, magenta, or yellow dye-donor layer, for example, can be placed face-to-face with a dye image-receiving layer of a receiver element to form a print assembly, which can be inserted between a thermal print head and a platen roller. A thermal print head can be used to apply heat from the back of the dye-donor sheet. The thermal print head can be heated up sequentially in response to the black, cyan, magenta, or yellow signals. The process can be repeated as needed to print all colors, and a laminate or protective layer, as desired. A color hard copy corresponding to the original picture can be obtained. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 to Brownstein.
In recent years the need has arisen to increase printing speed to satisfy customer demand. Various approaches have been adopted to achieve a higher printing rate. For example, a higher dye/binder ratio in combination with a reduced printing line-time can achieve satisfactory densities in a high-speed printing operation.
Such higher dye/binder ratios can, however, lead to quality problems following the manufacture of the dye transfer ribbons. When rolls of such ribbons are stored in the wound state, dyes can transfer to the slip layer provided on the back of the transfer sheet. This problem can occur in the manufacturing operation but is exacerbated under the conditions of high temperature and humidity that may occur sporadically in long-distance shipping operations. When such rolls are subsequently rewound into customer formats the transferred dye can be retransferred to the dye and protective layers on the donor sheet. At the time of printing onto an image receiving sheet, such contaminated layers produce colors which are different from those intended. Most objectionable is the noticeable stain in white areas of the print associated with undesirable dye transfer from the clear protective patch. Numerous attempts have been made to address this problem.
JP2000225775 teaches that a slip layer having greater than a specific surface roughness reduces dye transfer to the slip layer. Such increased surface roughness can lead to print head abrasion problems. JP02069292 proposes the use of a specific cyan dye to reduce retransfer but such dyes are not optimum in other respects. JP09300827 teaches the use of phosphate materials and polyvinyl acetal resins in the slip layer composition. JP11301125 proposes the use of a retransfer preventing layer on top of the protective laminate patch, where the resin employed in the retransfer preventing layer is the same as that in the laminate. JP11291645 teaches slip layer compositions comprising polysiloxanes and polyvinylacetal for reduced retransfer.
JP2000229483 proposes a slip layer composed of two sub-layers showing reduced coefficient of friction. The outer layer comprises acrylic, polyvinyl or phenoxy resins. JP2002011967 teaches slip layers for reduced transfer problems comprising resin, lubricants and polyisocyanate materials. U.S. Pat. No. 5,965,485 proposes a multilayer protective laminate structure to prevent retransfer of dye from slip layer to laminate which includes a low-dye-affinity top layer in the laminate. US 2005/0227023 teaches the use of dye binder resin comprising styrene-containing polyol resins.
Up till now, satisfactory retransfer properties combined with high speed printing of dyes showing excellent color reproduction and image stability have not been achieved.
Ser. No. 11/315,416 describes a magenta dye combination, a thermal donor including the magenta dye combination, and a method of forming thermal prints using the donor. The magenta dye compositions provide improved light stability and improved keeping properties, such as reduced or no crystallization. The magenta dye compositions further provides a more efficient dye composition, having a higher Dmax at certain voltage and line times.